Uniqlo and Primark share a verdict — both run small — but they earn it in opposite ways. Uniqlo runs small by design: Japanese fit blocks, slim through the chest and shoulders, short in the sleeve, and remarkably consistent about it. Primark runs small by tendency and is famously inconsistent on top — two identical garments can fit differently, and the brand even revised its chart in 2021 after complaints.
They also speak different sizing languages. Uniqlo uses alpha sizes built on US numerics; Primark labels in UK sizes (a Primark 12 is a US 8). That means letters and numbers can't be matched directly — so the tables below align the two brands by body measurement, which is the only conversion that holds up.
The short answer
It's close to a tie — both run small; Uniqlo is predictably slim, Primark is slim and a coin flip
Neither brand is the "bigger-fitting" one in any useful sense: both carry a runs-small verdict, and on the charts their measurements interleave rather than diverge. The honest difference is reliability. Uniqlo's fit blocks barely change between seasons — once you've sized up from your US size, your Uniqlo size holds. Primark's garment-to-garment consistency is loose enough that the chart is a starting point, not a guarantee, and even Primark staff recommend sizing up in denim.
Where each runs smallest: at Uniqlo it's the slim-fit lines (consider two sizes up) and anywhere sleeves and torso length matter, since both run short. At Primark it's jeans, fitted dresses, and tailored shirts — the standard advice is one size up in those, while basics and oversized tops sit closer to true to size. Convert between the brands through the bust and waist tables below, not through labels.
Uniqlo vs Primark at a glance
| Uniqlo | Primark | |
|---|---|---|
| Sizing system | Alpha sizes built on US numerics (M = US 8–10) | UK numeric sizes (a Primark 12 = US 8) |
| Overall fit | Runs small — slim Japanese fit blocks, deliberately | Runs small — sharpest in jeans, fitted dresses, tailored shirts |
| Consistency | Very consistent — your size holds season to season | Famously loose — identical garments can fit differently |
| Where to size up | Coming from US brands; two sizes in slim-fit lines | Denim above all — even Primark staff recommend it |
| Safe categories | Oversized lines (like many U collection pieces) — take your true size | Basics and oversized tops — closer to true to size |
Women's sizes aligned by bust
Rows are aligned by body bust measurement, not by label — Uniqlo uses US-based alpha sizes while Primark uses UK numbers, so labels can't be matched directly. Measurements from each brand's published chart.
| Uniqlo size | Uniqlo bust | Closest Primark | Primark bust |
|---|---|---|---|
| XS | 31–32" · 78–83 cm | UK 6–8 | 79 cm · 31" / 83 cm · 32.5" |
| S | 33–34" · 83–88 cm | UK 8–10 | 83 cm · 32.5" / 87 cm · 34.5" |
| M | 35–37" · 88–94 cm | UK 12 | 91 cm · 36" |
| L | 37–40" · 94–101 cm | UK 14–16 | 96 cm · 38" / 102 cm · 40" |
| XL | 40–43" · 101–109 cm | UK 16–18 | 102 cm · 40" / 109 cm · 43" |
| 2XL | 43–46" · 109–117 cm | UK 18–20 | 109 cm · 43" / 114 cm · 45" |
Women's waists at the aligned sizes
Same alignment by body measurement, this time on the waist. Note the closest Primark size can shift between bust and waist — Primark's chart grades the two differently, so check the measurement that matters for the garment.
| Uniqlo size | Uniqlo waist | Closest Primark | Primark waist |
|---|---|---|---|
| XS | 24–25" · 60–65 cm | UK 6 | 62 cm · 24.5" |
| S | 26–27" · 65–70 cm | UK 8–10 | 66 cm · 26" / 70 cm · 27.5" |
| M | 28–30" · 70–76 cm | UK 12 | 74 cm · 29" |
| L | 30–33" · 76–83 cm | UK 14 | 79 cm · 31" |
| XL | 33–36" · 83–91 cm | UK 16 | 85 cm · 33.5" |
| 2XL | 36–39" · 91–99 cm | UK 18–20 | 94 cm · 37" / 97 cm · 38" |
Men's tops side by side
Chest measurements at the same letter — Uniqlo publishes body measurements; Primark publishes to-fit chest figures and states its men's sizes are the same across UK, EU, and US. The bands track each other closely.
| Size | Uniqlo chest | Primark chest |
|---|---|---|
| XS | 32–35" · 81.5–89 cm | up to 36" · 90 cm |
| S | 35–38" · 89–96.5 cm | 36–38" · 91–96 cm |
| M | 38–41" · 96.5–104 cm | 38–40" · 97–102 cm |
| L | 41–44" · 104–112 cm | 41–43" · 103–108 cm |
| XL | 44–47" · 112–119.5 cm | 44–46" · 112–117 cm |
| XXL / 2XL | 47–50" · 119.5–127 cm | 47–49" · 119–124 cm |
Switching between Uniqlo and Primark
- Convert through body measurements, never labels — Uniqlo's letters are US-based while Primark's numbers are UK sizes, which run four numbers higher than US.
- Apply each brand's own size-up rule on top of the conversion: slim-fit lines at Uniqlo, and jeans, fitted dresses, and formal shirts at Primark.
- At Primark, check the measurements on the garment label, not just the size — consistency varies piece to piece, so the chart is only a starting point.
- At Uniqlo, watch lengths instead — sleeves and torsos run short, so taller shoppers should check garment lengths on the product page.
Measurements are based on each brand's published size charts and may vary by garment, fabric, and region. For the full charts and fit notes, see the Uniqlo size guide and the Primark size guide.
Uniqlo vs Primark sizing FAQs
Which runs smaller, Uniqlo or Primark?
It's genuinely close — both run small. Uniqlo is slim by design and very consistent about it; Primark tends small in fitted styles (jeans, dresses, tailored shirts) and is inconsistent garment to garment. The practical difference is that a sized-up Uniqlo order lands predictably, while a Primark order is more of a lottery.
What Primark size matches my Uniqlo size?
Convert by measurement: Uniqlo S (33–34" bust) lands around a Primark UK 8–10, Uniqlo M (35–37") around a UK 12, and Uniqlo L (37–40") around a UK 14–16. Then apply Primark's own rule — size up one in jeans, fitted dresses, and formal shirts.
Why can't I just match the size labels?
Because the systems don't line up. Uniqlo's alpha sizes are built on US numerics (its M is a US 8–10), while Primark labels in UK sizes, which run four numbers higher than US — a Primark 12 is a US 8. Matching an M to a 12 only works once you've converted through the actual body measurements.
Which brand is the safer online or blind buy?
Uniqlo, comfortably. Its fit blocks barely change between seasons, so once you know your (usually sized-up) Uniqlo size it holds across categories. Primark's garment-to-garment consistency is loose — two copies of the same piece can measure differently — so in-store try-on or checking the label's measurements matters more there.
Do both brands run small in menswear too?
The men's charts track each other closely — Uniqlo's M covers a 38–41" chest against Primark's 38–40" — so on paper there's little between them. Uniqlo's cut is slim through the shoulders and sleeves, and Primark's fitted shirts carry its size-up reputation, so men between sizes should go up at either brand.
